MarkBour wrote:That is one gorgeous image, especially at the higher resolution.
Thanks to my tutelage in this forum, I have a new appreciation for the dust lanes in this image. Whereas I used to envision them quite differently, I now see them as material that has come from the stars. Where there is high density of stars, this dust gets blown away above and below the galactic disk. (Somewhat like smoke from a fire.) This image would go along with that thought. The dust lanes appear to coincide with the areas of rich star formation, i.e. the spirals.
Incidentally, it looks to me as though NGC 1398 has basically two spiral arms. Would other readers agree with that?
I agree that it looks as if NGC 1398 has two prominent inner arms (and now I'm not talking about the inner ring). The inner arms are relatively long and thin. ON the right-hand side of the image, we can see what looks like three arms winding around the main body of the galaxy. But on the left-hand side, the arms appear to break up into numerous little "arm-lets".
Would these be considered tightly wound?
Absolutely! The arms are tightly wound. NGC 1398 is classified as Hubble class SBab, or so I think. That means that the galaxy is a spiral with a bar, a large bulge and tightly wound arms. The galaxies with loose arms are classified as Hubble class Sc or even Sd.
If so, I note that one of the arms is far thicker and more "feathered" than the other. The APOD caption suggests that the inner ring is perhaps expanding outward. I wonder how it will change over a very long time.
Well, one possibility is that, in the very long run, NGC 1398 will run out of gas completely, and all star formation will stop. The dust will spread out too and become invisible. So in the very long run, NGC 1398 may look like NGC 936, here photographed
by SDSS SkyServer.
A final question for today. In this image, the spirals appear to have both pink and blue granules in them (close-up at right).
At a distance of 65 M Ly, I wonder what we are able to see that appears this way. Is every one a cluster, or can they be lesser collections of star population, but perhaps still regions of higher-than-average stellar density?
The filters used for this image are blue, green, red and H-alpha. The H-alpha filter makes the emission nebulas stand out strongly. So we have every reason to believe that the pink splotches represent pink emission nebulas like, for example, the Orion Nebula.
The blue blobs are young star clusters.